Previously, sleuth logged more data than necessary. This led to issues
including spans approaching megabytes each. This pares down default keys
to a minimal set, but allows users to opt-into logging more by extending
`TraceFilter`.
- Changed Random instantiation to a shared Random
- Changed the name of the converter
- Changed generator into random
- Span id is now non-nullable.
- it gets generated in the http filter if it's not there
- it's generated in the spring-integration channels if it wasn't set
It's not really necessary to use rabbit, but the existing tests
weren't really using the stream components at all because
zipkin spans were being collected by spring-cloud-sleuth-zipkin.
